In view of the advantages of the bulk production of clonal pancreatic beta cells, an investigation was made of the growth and insulin secretory functions of an electrofusion-derived cell line (BRIN-BD11) immobilized on a solid microcarrier, cytodex-1 or a macroporous microcarrier, cultispher-G. For comparison, similar tests were performed using BRIN-BD11 cells present in single cell suspensions or allowed to form pseudoislets. Similar growth profiles were recorded for each microcarrier with densities of 4.4 x 10(5) +/- 0.3 cells/ml and 4.2 x 10(5) +/- 0.2 cells/ml achieved using cytodex-1 and cultispher-G, respectively. Cell viability began to decline on day 5 of culture. Insulin concentration in the culture medium reached a peak of 26 +/- 2.0 ng/ml and 24 +/- 2.2 ng/ml for cells grown on cytodex-1 and cultispher-G, respectively. Cells grown on both types of microcarrier showed a significant 1.5-1.8-fold acute insulin-secretory response to 16.7 mmol/l glucose. L-alanine (10 mmol/l) and L-arginine (10 mmol/l) also induced significant 3 4 fold increases of insulin release. BRIN-BD11 cells immobilized on cytodex-1 or cultispher-G out-performed single cell suspensions and pseudoislets in terms of insulin-secretory responses to glucose and amino acids. A 1.3-fold, 2.2-fold and 1.7-fold stimulation of insulin secretion was observed for glucose, L-alanine and L-arginine respectively in single cell suspensions. Corresponding increases for pseudoislets were 1.6-1.8-fold for L-alanine and L-arginine, with no significant response to glucose alone. These data indicate the utility of micro-carriers for the production of functioning clonal beta cells.